Porous materials, because of their useful structural and chemical properties, have been heretofore researched, developed and used in various fields for various applications as packings for analytical or preparative columns, carriers for enzymes or catalysts, supports for adsorbing valuable substances such as medicines, and so on. Typical examples are inorganic materials such as porous silica gel and alumina, and synthetic polymer materials such as divinylbenzene-styrene porous resins and divinylbenzene-methacrylate porous resins.
Silica gel, which has high mechanical strengths, is widely used. It is used by itself mainly as a column packing for normal phase systems, and silica gel to which a long-chain alkyl group is introduced by utilizing a silanol group on its surface is used mainly as a column packing for reversed-phase systems. However, silica gel has problems associated with its inherent chemical stability level, namely a low stability in a basic medium, the influence of residual silanol group or the influence of metals in trace amounts cf., e.g., J. Chromatogr. Sci., vol.22, p.386 (1984) and J. Chromatogr. vol.149, p.199 (1978)!.
Divinylbenzene-styrene porous resins are excellent both in mechanical strengths and chemical stabilities, and has been researched and developed in the field of and for the application as column packings cf., e.g., J. Chromatogr. Sci, vol.22, p.386 (1984) and J. Chromatogr., vol.442, p.97 (1988)!. Various kinds of the resins are commercially available as polymer-type column packings for reversed-phase systems. Basic processes for preparing divinylbenzene-styrene porous resins have been long known. For example, according to a known process, a monomer mixture comprising divinylbenzene, styrene, etc. is mixed with an organic solvent, and the obtained solution is subjected to a suspension polymerization in water using a radical polymerization initiator. The organic solvent is what is called a porogen which does not participate in the polymerization, is sparingly soluble in water, is capable of solving the monomer mixture but is incapable of solving the resulting copolymer cf., e.g. J. Appl. Polym. Sci., vol.23, p.927 (1979) and Angew. Makromol. Chem., vol.80, p.31 (1979)!. Generally, this type of porous resin prepared by a suspension polymerization is of the order of .mu.m to mm in the diameter of apparent particles (hereinafter referred to as "secondary particles"). The secondary particles, when externally or internally observed under an electron microscope, are seen to be firm aggregates of finer particles having a size of the order of nm (hereinafter referred to as "primary particles"). Stated more specifically, the interstices between aggregated primary particles are hollows which have been occupied by the organic solvent during the polymerization. The primary particles, which are highly crosslinked resin particles, are insoluble in most of organic solvents and are substantially free from swelling. The porous resins prepared by this process have a large specific surface area, high mechanical strength and high chemical stability, and therefore are widely used as supports in many fields, column packings for analytical or preparative purposes, etc.
However, a column packed with the divinylbenzene-styrene porous resin generally has considerably inferior performance to a column packed with silica gel. In particular, divinylbenzene-styrene porous resins are poor in the chemical or structural variations on their surfaces (such as control of hydrophobic or hydrophilic properties, control of stereostructures, etc.), and thus have problems that they lack flexibility for use as packings or as supports for useful substances.